EP0707609A1

EP0707609A1 - Curing agents for aqueous epoxy resins

Info

Publication number: EP0707609A1
Application number: EP94920727A
Authority: EP
Inventors: Jason L. Chou; Shailesh Shah; Brian G. Jewell; Robert M. Moon
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1993-06-30
Filing date: 1994-06-15
Publication date: 1996-04-24
Also published as: JPH08512079A; WO1995001386A1; US5583167A; MY130053A; EP0707609A4; SG52534A1; AU7172594A

Abstract

Provided are epoxy curing agents comprising the reaction product of reactants consisting essentially of an alkylene polyamine having less than about 12 carbon atoms, an aromatic mono-glycidyl ether having less than about 18 carbon atoms, and a diglycidyl ether of an aromatic diol having an average degree of oligomerization of less than about 3.5, wherein the ratio of primary amine equivalents of said alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol is not essentially less than one, and the ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is greater than one. The reaction product is preferably employed as a curing agent for an aqueous epoxy resin in a two component coating system wherein said curing agent, essentially free of acids, is mixed with an aqueous epoxy resin emulsion and then the resulting mixture is applied as a continuous coating to a rigid substrate, e.g. as an industrial maintenance coating.

Description

CURING AGENTS FOR AQUEOUS EPOXY RESINS

Field of the Invention

The present invention relates to curing agents for aqueous epoxy

resins and to their use. More particularly, it relates to the reaction product

of polyamines with glycidyl ethers that are useful as curing agents for

aqueous epoxy resin emulsions, which cured resins are, in turn, useful as protective coatings.

Background of the Invention

Solvent based, epoxy resin curing agent systems have been known

for many years. However, these solvent systems often are quite flammable

and many exhibit disagreeable odors. In recent years, increasingly strict

regulation of environmental pollutants has lead to a limitation on the types

and amounts of organic solvents which can be used in epoxy resin curable systems. The first approach to these limitations on the solvent content of coating systems was simply to employ a surfactant and emulsify or disperse existing solvent-based polymeric systems in water. Examples of such

systems include U.S. Patent No. 3,301 ,804 which discloses the use of the

reaction product of boric acid, an alkylene glycol, and a beta-dialkyl-

substituted aminoalkanol as an emulisfier, U.S. Patent No. 3,634,348

which discloses the use of a phosphate ester as an emulsifying agent, and

U.S. Patent No. 3,249,412 which discloses the use of a combination of a cationic emulsifying agent, selected from the group consisting of

imidazolines and amides, and a non-ionic emulsifying agent.

However, the cured products which result from these emulsions or

dispersions may exhibit poor properties when compared to prior art

solvent-based systems. In particular, the chemical and water resistance of

such systems may be lower because of the high levels of surfactant which

were needed. U.S. Patent No.4, 166,900 discloses cathodic electrodeposition resins

prepared based upon polyepoxides, polyamines and monoepoxides.

Polyepoxide resins are adducted with polyamines which are further reacted

with a monoepoxide or a monocarboxylic acid. It is disclosed that the

resinous adducts are water soluble or water dispersible when salted with an

acid. It is also stated that the resin solutions or dispersions are particularly

useful in cathodic electrodeposition processes for prime coating metal

objects.

U.S. Patent No. 4,246,148 discloses a two component industrial

maintenance coating. The first component is a polyamine terminated epoxy resin which is end capped with a monoepoxide, at least 25 mole percent of the monoepoxide being an aliphatic monoepoxide. The second component

is a low molecular weight polyepoxide crosslinker. It is disclosed that the

adduct can be dissolved or dispersed in water when salted with an acid. The

polyepoxide crosslinker can then be microemulsified in the system. When

coated on a substrate, the two component mixture is said to cure at room

temperature producing coatings having a balance of chemical and physical

properties.

U. S. Patent No. 4, 608,405 discloses an ambient temperature curing

agent used to cure epoxide resins. The curing agent preferably is prepared

by coreacting under liquid advancement conditions, a diglycidyl ether of a dihydricphenol, a diglycidyl ether of an aliphatic dihydroxy polyether and a

dihydricphenol to produce a product having an average weight per epoxide

(WPE) of about 400 to about 1300. Substantially all of the epoxy groups which remain in the advanced product are then reacted with a polyamine

and at least each primary amine group of the polyamine/diepoxide reaction

product is further reacted with a monoepoxide or a monocarboxylic acid. It

is stated that these curing agents may be salted with a volatile acid and

employed in aqueous systems to provide coatings having superior cured

states film properties. It is also stated that, while the preparations of these

curing agents by the liquid advancement process is preferred, it is also

possible to prepare similar curing agents by starting with the corresponding

dihydric phenol and aliphatic dihydroxy polyether and epoxidizing this

mixture using well known epoxidization techniques. Summary of the Invention

This invention relates to epoxy curing agents comprising the reaction

product of reactants consisting essentially of:

an alkylene polyamine having less than about 12 carbon atoms

(preferably a member selected from the group consisting of lower alkylene

diamines and lower polyalkylene polyamines, said member having from 2 to

8 carbon atoms and, more preferably, only straight-chain alkylene groups),

an aromatic mono-glycidyl ether having less than about 18 carbon

atoms (preferably selected from the group consisting of mono-alkylphenyl

glycidyl ethers and di-alkyl phenyl glycidyl ethers having from 9 to 13 carbon atoms), and

a diglycidyl ether of an aromatic diol having an average degree of

oligomerization of less than about 3.5 (preferably less than about 1.5, and

preferably derived from an alkyl bis-phenol, e.g. bisphenol A), wherein:

the ratio of primary amine equivalents of said alkylene polyamine to

the total epoxide equivalents of said aromatic glycidyl ether and said

diglycidyl ether of an aromatic diol are not less than essentially one, and

the ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is greater

than one (preferably greater than 1 .5, more preferably from about 2:1 to

about 6:1 , and most preferably from about 3:1 to 5:1 ). In preferred

embodiments, the alkylene polyamine is not pre-reacted with the diglycidyl

ether of an aromatic diol and, thus, said ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is at no time during the entire course of the reaction, less

than the final product ratio of epoxide equivalents of said aromatic mono- glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic

diol. (By "final product ratio" is meant the ratio of all epoxide equivalents

of said aromatic mono-glycidyl. ether added over the entire course of the

reaction to all epoxide equivalents of said diglycidyl ether of an aromatic diol

added over the entire course of the reaction.) The maintenance of such a

ratio can accomplished by co-addition of proportionally adjusted amounts

said aromatic mono-glycidyl ether and said diglycidyl ether of an aromatic

diol (which will maintain the final product ratio essentially throughout said

reaction) or by pre-reacting the mono-glycidyl ether with the alkylene

polyamine (which will maintain an even greater ratio than the final product

ratio for most of the course of the reaction).

This invention also relates to a first group of preferred embodiments

within the broad scope set forth above wherein the alkylene polyamine is a

polyalkylene polyamine and the ratio of primary amine equivalents of said

alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol is essentially one, i.e. the

molar equivalents of primary amine groups of said polyalkylene polyamine

is essentially equal to the molar equivalents of glycidyl groups (e.g. a ratio

of from about 0.85: 1 to about 1 .05: 1 , preferably from about 0.90: 1 to

about 0.95:1 ). This invention further relates to a second group of preferred embodiments within the broad scope set forth above, wherein the alkylene

polyamine is a mono-alkylene polyamine and the ratio of primary amine

equivalents of said alkylene polyamine to the total epoxide equivalents of

said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol is

greater than essentially one, i.e. the molar equivalents of primary amine

groups of said polyalkylene polyamine are essentially in excess of the molar

equivalents of glycidyl groups (e.g. a ratio of from about 1.05:1 to 2.0:1 ,

preferably from about 1.1 :1 to about 1 .75: 1 , more preferably from about

1.2: 1 to about 1.5:1 ).

This invention also relates to a third group of preferred embodiments

wherein said alkylene polyamine is comprised of a major amount on a molar

basis of a mono-alkylene polyamine and a minor amount on a molar basis of a polyalkylene polyamine (preferably in a molar ratio of from about 6: 1 to

about 2.5:1 , more preferably from about 5: 1 to about 3:1 ).

The reaction product is preferably employed as a curing agent for an

aqueous epoxy resin in a two component coating system wherein said

curing agent, essentially free of acids, is mixed with an aqueous epoxy resin

emulsion and then the resulting mixture is applied as a continuous coating

to a rigid substrate.

Detailed Description of the Invention

The curing agents of this invention are prepared from three major reaction components. The first component is an alkylene polyamine, the second component is an aromatic glycidyl ether, and the third component

is diglycidyl ether of an aromatic diol. The nature of these components will

be addressed in turn below.

The alkylene polyamines useful in this invention can be characterized

as lower alkylene polyamines and lower polyalkylene polyamines. These

materials are commercially available or can be prepared by conventional

preparative techniques. These contain at least 2 amine nitrogen atoms per

molecule, at least 3 amine hydrogen atoms per molecule and no other

groups which are reactive with epoxide. Useful polyamines typically contain

about 2 to about 6 amine nitrogen atoms per molecule, 3 to about 8 amine

hydrogen atoms, and 2 to about 12 carbon atoms. Mixtures of amines can

also be used.

Examples of such amines are the alkylene polyamines ethylene

diamine, 1 ,2-propylene diamine, 1 ,3-propylene diamine, 1 ,2-butylene

diamine, 1 ,3-butylene diamine, 1 ,4-butylene diamine, 1 ,5-pentylenediamine,

1 ,6-hexylene diamine, 1 ,7-heptylene diamine, 1 ,10-decylene diamine, and

the like. Preferred amines for use in this invention are polyamines of the formula H₂N-R(-NH-R)_n-NH₂ wherein n is 0 to 4 and R is an alkylene group

containing 2 to 8 carbon atoms, provided the total carbon atoms do not

exceed 12. Examples of the preferred mono-alkylene polyamines include

1 ,4-butylene diamine (tetramethylene diamine), 1 ,6-hexylene diamine

(hexamethylene diamine), and 1 ,8-octylene diamine (octamethylene

diamine) . The polyalkylene polyamines have at least one secondary amine

group. Examples of polyalkylene polyamines include diethylene triamine, triethyiene tetramine, tetraethylene pentamine, pentaethylene hexamine,

dipropylene triamine, tributylene tetramine, trimethylhexamethylene diamine,

hexamethylene triamine and the like. The more preferred polyalkylene

polyamines are the polyethylene polyamines with the most preferred being

triethyiene tetramine and diethylene triamine.

Cyclic diamines can also be included in the diamine component,

preferably, however only in minor amounts, e.g. at less than 10%, and

preferably less than 5%, of the primary amine equivalents. Examples of

cyclic diamines include 1 ,4-diaminocyclohexane, 1 ,2-diaminocyclohexane,

o, m and p-phenylene diamine, 4,4'-methylene dianiline, meta-xylylene

diamine, and isophorone diamine.

In certain embodiments of the invention, the amine component is

comprised of a major amount on a molar basis of a mono-alkylene polyamine

and a minor amount on a molar basis of a polyalkylene polyamine (preferably

in a molar ratio of from about 6:1 to about 2.5:1 , more preferably from

about 5:1 to about 3: 1 ). It has been found that the use of both a mono-

alkylene polyamine and a polyalkylene polyamine has certain advantages

over the use of a mono-alkylene polyamine alone. One important advantage

is that the polyalkylene polyamine appears to prevent precipitation of the

curing agent that can occur upon storage. Without wishing to be bound by

any theory, unless expressly noted otherwise, it is thought that the

molecular structure of a mono-alkylene polyamine, such as hexamethylene

diamine, may allow the molecular species of curing agent prepared

therefrom to associate in a manner that allows the curing agent to crystallize or otherwise precipitate. The use of an amount of a polyalkylene polyamine in an amount sufficient to inhibit such precipitation (e.g. a molar ratio of

mono-alkylene polyamine to polyalkylene polyamine of less than about 4:1 )

thus allows one of ordinary skill to extend the shelf life of the curing agent,

if so desired.

The polyepoxide materials useful in this invention are glycidyl

polyethers of dihydric phenols and contain, on average, more than one, but

not more than two 1,2-epoxide groups per molecule. Such polyepoxide

materials are derived from an epihalohydrin and a dihydric phenol and have

an epoxide equivalent weight of about 100 to about 4000, preferably from

about 125 to about 525, and more preferably from about 150 to about 350. Examples of epihalohydrins are epichlorohydrin, epibromohydrin and

epiiodohydrin with epichlorohydrin being preferred. Dihydric phenols are

exemplified by resorcinol, hydroquinone, p,p'-dihydroxydiphenylpropane (or

Bisphenol A as it is commonly called), p,p'-dihydroxybenzophenone,

p,p'-dihyd roxydipheny I, p,p'-dihydroxy pheny I ethane,

bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthaleneandthe like with

Bisphenol A being preferred.

These polyepoxide materials are well known in the art and are made in desired molecular weights by reacting the epihalohydrin and the dihydric

phenol in various ratios or by reacting a dihydric phenol with a lower

molecular weight polyepoxide material. Preferred polyepoxide materials are

glycidyl polyethers of Bisphenol A having epoxide equivalent weights of

about 150 to about 525 and, thus, have from just greater than 1.0 (e.g. from about 1 .1 ) to just less than 3.5 (e.g. up to about 3.4) dihydric phenol groups per polyether molecule, and more preferably have epoxide equivalent

weights of less than 400.

The third component is an aromatic mono-glycidyl ether, i.e., a

compound having at least one aromatic ring having attached thereto an

glycidyl functional group and no other reactive functional groups.

Representative examples of aromatic mono-glycidyl ethers include the

monoglycidyl ethers of monohydric aromatic alcohols such as phenol and

naphthanol, mono- or dialkyl-substituted monoglycidyl ethers of monohydric aromatic alcohols, said alkyl groups having from about 1 to about 4 carbon

atoms, such as the monoglycidyl ether of o-cresol, m-cresol, p-cresol, o- ethyl-phenol, m-ethyl-phenol, p-ethyl-phenol, o-(n-propyl)-phenol, m-(n-

propyD-phenol, p-(n-propyl)-phenol, o-isopropyl-phenol, m-isopropyl-phenol,

p-isopropyl-phenol, o-(n-butyl)-phenol, m-(n-butyl)-phenol, p-(n-butyl)-

phenol, m-(t-butyl)-phenol, p-(t-butyl)-phenol, 2,4-dimethyl-phenol, 3,5-

dimethyl-phenol, 3-methyl-5-ethyl-phenol, 2-methyl-4-(n-propyl)-phenol, or

2-methyl-4-(t-butyl)-phenol. The preferred aromatic mono-glycidyl ether is o-cresyi glycidyl ether.

The ratios of the reactants are selected so that the primary amine

equivalents of said alkylene polyamine to the total epoxide equivalents of

said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol are

essentially equal. This means that, on average, all of the primary amine

groups will be converted to secondary amines (i.e. a group still having a

reactive secondary amine hydrogen, albeit less reactive than a primary amine hydrogen). Preferably less than 10% and more preferably less than 5% of primary amine hydrogens will remain in the curing agent.

As discussed above, in preferred embodiments, the alkylene

polyamine is not pre-reacted with the diglycidyl ether of an aromatic diol

and, thus, said ratio of epoxide equivalents of said aromatic mono-glycidyl

ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is at no time during the entire course of the reaction, no less than the final

product ratio of epoxide equivalents of said aromatic mono-glycidyl ether to

epoxide equivalents of said diglycidyl ether of an aromatic diol. (By "final

product ratio" is meant the ratio of all epoxide equivalents of said aromatic mono-glycidyl ether added over the entire course of the reaction to all epoxide equivalents of said diglycidyl ether of an aromatic diol added over

the entire course of the reaction.) The maintenance of such a ratio can

accomplished by co-addition of proportionally adjusted amounts said

aromatic mono-glycidyl ether and said diglycidyl ether of an aromatic diol

(which will maintain the final product ratio essentially throughout said reaction) or by pre-reacting the mono-glycidyl ether with the alkylene

polyamine (which will maintain an even greater ratio than the final product

ratio for most of the course of the reaction). Of course, because of the possibility of differing rates of reactivity with the alkylene polyamine, the

ratio of mono-glycidyl ether to aromatic diol may vary somewhat over time

in the reaction medium. Because the mono-glycidyl ether is present in the

reaction from the beginning of the reaction, however, the resulting reaction

product will have a relatively smaller degree of polymerization, for example, as compared with the use of a mono-glycidyl ether solely as a capping agent for an adduct of a polyamine and a polyepoxide.

Moreover, the ratio of epoxide equivalents of said aromatic mono¬

glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic

diol is greater than 1 , preferably greater than 1.5, and more preferably from

about 2:1 to about 6:1 , and most preferably from about 3:1 to 5: 1 . Thus,

the reaction product will be comprised predominantly (e.g. greater than 60%

by weight) of species derived from the reaction of two mono-glycidyl ether

molecules with one alkylene polyamine and only a minor amount (e.g. less

than 35% by weight) of species derived from the reaction of one diglycidyl

ether of an aromatic diol with two alkylene polyamine molecules and two aromatic mono-glycidyl ether molecules. Further, because the secondary

amine hydrogen atoms of a polyalkylene polyamine are reactive, there is the possibility for some branching of the molecule, but use of a relatively high

ratio of mono-glycidyl ether to diglycidyl ether of an aromatic diol (optionally

along with a low reaction temperature) will reduce such a possibility

dramatically, such that the reaction product will be essentially free of

branched species.

While not wishing to exclude any other components unnecessarily, it

is noted that the use of glycidyl ethers of polyoxyalkylenes and/or volatile

acids to salt the curing agent are not needed in the curing agent and so

should be excluded. Further, it is believed that the selection of components

is so important to the performance of the curing agent that other

components which would affect the essential attributes of the curing agent, or cured epoxy resins prepared therefrom, should be excluded. The skilled

artisan will, with the aid of the following description, be able to determine

whether a particular component in a particular amount will affect the

attributes of the curing agent in an essential manner, i.e. will prohibit its use

as a curing agent for an aqueous epoxy emulsion used to prepared a protective coating when cured.

The reaction medium is typically maintained at moderate temperatures

during the reaction. Such temperatures avoid degradative side reactions

which can affect the appearance (e.g. by excessive color formation) of the

reaction product. Typical temperatures that will be maintained during the reaction range from about 35 °C. to about 80°C, preferably from about

40°C to about 75 °C, for a time sufficient to bring the reaction to

completion, typically about 5 minutes to 3 hours. Lower temperatures may

be employed at the expense of increasing the reaction time. The reaction

medium is also typically treated to exclude oxygen to a practicable degree,

e.g. by blanketing and/or sparging the reaction zone with an inert gas, e.g.

dry nitrogen.

The product which results after the epoxide material has been reacted

with the polyamine is extremely viscous and it is preferred that an

oxygenated solvent be present in the reaction medium or added to the

reaction product to reduce its viscosity. The preferred solvents are the

glycol ethers such as the various lower alkyl ethers of ethylene and

propylene glycol. Typically, about 20 to about 50 percent by weight of an alkoxy-alkanol, e.g. 2-propoxy ethanol, or another oxygenated solvent may

be used.

The second major component of the coating system is a water

dispersible (either alone or in the presence of a co-solvent) epoxy resin

having more than one terminal epoxide group. The epoxy resins suitable for use in the second component include the glycidyl polyethers of dihydric

phenols as well as epoxy novolac resins. The dihydric phenols employed to

prepare the epoxy resins are further described in U.S. Pat. No. 4,246,148.

It is particularly preferred to employ those glycidyl polyethers wherein the

dihydric phenol is bisphenol-A. Examples of suitable resins include those disclosed in U.S. Patent No. 4,315,044, the disclosure of which is

incorporated herein by reference. Particularly preferred epoxy resins are

those disclosed in U.S. Serial No. (Case No. M 5308 FPD/CO), filed

concurrently herewith, the disclosure of which is incorporated by reference.

The maximum molecular weight of the epoxy resins is limited by the fact that the amount of epoxy resin employed in the second component is

usually selected to achieve stoichiometric equivalence of epoxy groups with

the amine hydrogen equivalents of the curing agent. Consequently, as the

molecular weight of the epoxy resin increases, thereby increasing the

epoxide equivalent weight, more of the epoxy resin is required to satisfy the

stoichiometric requirement. However, the use of large amounts particularly

of higher molecular weight epoxy resins is not preferred because they are

water insoluble and become increasingly more difficult to microemulsify or

disperse as the amount thereof is increased. In view of the above, it is preferred to characterize the epoxy resin

also in terms of its epoxide equivalent weight. Thus, the epoxide equivalent

weight (WPE) of the glycidyl polyethers of dihydric phenols is not greater

than about 1000, preferably from about 180 to about 700.

As described above, the amount of epoxy resin which is present in

the coating composition is preferably sufficient to achieve substantially

stoichiometric equivalence with the reactive amino hydrogens on the end

capped epoxy-amine adduct. In general, it is preferred to employ the epoxy

resin in an amount sufficient to achieve an epoxy to reactive amine

hydrogen equivalent weight ratio of from about 0.5: 1 .0 to about 1 .5:1 .0,

and, preferably, from about 0.8:1.0 to about 1.2:1.0.

The epoxy resins which are useful herein, may be either liquids or

solids, so long as the resin is in the form of a stable aqueous dispersion.

Preferred aqueous epoxy resins are disclosed in U.S. patent application Serial No. (Case No. M5308), filed on even date herewith, entitled "Self-Dispersing

Curable Epoxy Resins, Dispersions Made Therewith, And Coating

Compositions Made Therefrom", by John G. Papalos et al., the disclosure

of which is incorporated herein by reference.

When the epoxy resin and the curing agent are mixed, the resulting

coating composition exhibits a useful pot life at room temperature, e.g. from

about 2 hours to about 12 hours, and more typically from about 3 hours to

about 8 hours. The pot life of the coating composition is herein defined to

be the elapsed time from mixing the components together until the resulting

composition is no longer suitable, with normal thinning, for application by spray, brush, or roll coating techniques to a substrate. The suitability for

application by common techniques can be expressed in terms of the

viscosity of the coating composition. Thus, the pot life of unpigmented

coatings can be characterized as the elapsed time from mixing the two

components to the time when the viscosity of the coating compositions

drops below A1 or increases above Z6 as determined by the Gardner-Holdt

method. For pigmented coatings, useful applications viscosities are between

50 and 140 Kreb Units (K.U.) as determined with a Stormer viscometer.

Coatings based on the compositions described herein can be

formulated into easily handled two-package systems which blend together

as easily as their solvent based counterparts. Application by brush, spray

and roller-coating are typically free of bubbling and other film imperfections.

The coating systems described herein should also exhibit good

adhesion to such widely varied substrates as galvanized metal, cold rolled steel (untreated and phosphate treated), hot rolled steel, and aluminum.

Flash rusting is not a problem over untreated steel and, therefore, there is

no need for special additives as in some water reducible epoxy systems.

Adhesion should also be excellent to three and four-year old alkyd and epoxy

ester enamel films. Such systems may therefore be employed for repaint

purposes in food processing plants and dairies and can also be used as

adhesive compositions per se.

As pointed out above, a major advantage of the coating compositions

of the instant invention is that they are useful in preparing solvent and

chemically resistant coating compositions from aqueous based systems. These systems do not exhibit the traditional solvent related problems shown by solvent based systems and accordingly are preferred in end-use

applications where nonpolluting or nonflammable coatings systems are

necessary. In addition, the cured state properties of compounds made from

the curing agents disclosed herein are generally equivalent or superior to the

properties of compounds prepared from prior art solvent based systems.

The following examples will serve to further illustrate the invention,

but should not be construed to limit the invention, unless expressly set forth

in the appended claims. All parts, percentages, and ratios are by weight

unless otherwise indicated in context.

EXAMPLES

EXAMPLES 1-4

Curing agents were prepared by charging to a flask the amine

reactants diethylenetriamine (DETA), 1 ,2-diamino-cyclohexane (DACH),

hexamethylenediamine (HMDA) in the molar amounts set forth Table 1 ,

below, along with the solvent 2-propoxyethanol, with mixing and under dry

nitrogen gas. The contents were heated to 40°C. The epoxide reactants

cresyl glycidyl ether (CGE) and a bisphenol A diglycidyl ether homopolymer

having an average of 1.15 bisphenol A groups per molecule and available from the Dow Chemical Co. as DER 331 , were pre-mixed in the molar

amounts shown in Table 1 and the pre-mixture was added dropwise to the

charge flask to maintain the temperature within the flask to less than 70°C. Once the addition of epoxide reactants was complete, the flask was held at

50°C for about 2 hours.

Table 1 Curing Agent Composition

Example DETA DAGH HMDA CGE DER 331 (moles) (moles) (moles) (moles) (moles)

1 1.00 0.04 0.04 1.72 0.22

2 1.00 0.04 0.04 1.30 0.43

3 0.17 0.03 0.80 0.96 0.12

4 0.17 0.03 0.80 1.20 0.15

Example 5

The curing agent of Example 1 was used to cure an epoxy resin from

an aqueous dispersion as follows. The epoxy resin dispersion of Example 3 of U.S. patent application Serial No. (Case M5308 FPD/CO), referred to

above, in an amount of 200 parts by weight was ground with 123.7 parts

by weight of titanium dioxide pigment (DuPont R-960) along with 17 parts

by weight of oxygenated solvent (Ektasolve EP), and 103.9 parts by weight

of water. To this grind paste was added 44.7 parts by weight of the curing

agent of Example 1 , above. The resulting white epoxy paint thus had a ratio

of epoxy equivalents to active amine hydrogen equivalents of 1 :1 , a pigment

to binder ratio of 0.85:1 , and 55% non-volatiles (by calculation). This

coating composition was applied to cold rolled steel at a thickness of 56

micrometers to 62 micrometers. The coating was cured at room temperature for 14 days and then evaluated. The cured coating exhibited a Crosshatch adhesion of 100% (5B), a pencil hardness of HB, Impact

Direct/Reverse strength of 160/120 in-lbs., passed the conical mandrel test,

survived 500 methyl ethyl ketone double rubs, and exhibited no salt spray corrosion until about 500 hours. This performance was superior to a

commercial water-borne epoxy resin (Epi-Rez WJ-5522 cured with CMD J60-8290, both available from_. Hi-Tek), but still inferior in a number of

respects to a solvent-borne epoxy resin DER 671X75, available from Dow

Chemical Co. cured with Versamid 115, available from Henkel Corporation,

Ambler, PA).

Claims

WHAT IS CLAIMED IS:

1. An epoxy curing agent comprising the reaction product of reactants

consisting essentially of an alkylene polyamine having less than about 12

carbon atoms, an aromatic mono-glycidyl ether having less than about 18 carbon atoms, and a diglycidyl .ether of an aromatic diol having an average

degree of oligomerization of less than about 3.5, wherein:

the ratio of primary amine equivalents of said alkylene polyamine to the

total epoxide equivalents of said aromatic glycidyl ether and said diglycidyl ether

of an aromatic diol is not essentially less than one, and

the ratio of epoxide equivalents of said aromatic mono-glycidyl ether to

epoxide equivalents of said diglycidyl ether of an aromatic diol is greater than

one.

2. An epoxy curing agent of claim 1 wherein said aromatic mono-glycidyl

ether is selected from the group consisting of mono-alkylphenyl glycidyl ethers

and di-alkyl phenyl glycidyl ethers having from 9 to 13 carbon atoms.

3. An epoxy curing agent of claim 1 wherein said diglycidyl ether of an

aromatic diol having an average degree of oligomerization of less than about

1.5.

4. An epoxy curing agent of claim 1 wherein said diglycidyl ether of an aromatic diol is derived from an alkyl bis-phenol. 5. An epoxy curing agent of claim 1 wherein the ratio of epoxide

equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said

diglycidyl ether of an aromatic diol is greater 1.

5.

6. An epoxy curing agent of claim 1 wherein the ratio of epoxide

equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said

diglycidyl ether of an aromatic diol is from about 2:1 to about 6:1 .

7. An epoxy curing agent of claim 1 wherein the ratio of epoxide

equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said

diglycidyl ether of an aromatic diol is from about 3:1 to 5:1.

8. An epoxy curing agent of claim 1 wherein said ratio of epoxide

equivalents is maintained essentially throughout said reaction by co-addition of

said aromatic mono-glycidyl ether and said diglycidyl ether of an aromatic diol.

9. An epoxy curing agent wherein said alkylene polyamine is a member

selected from the group consisting of lower alkylene diamines and lower

polyalkylene polyamines, said member having from 2 to 8 carbon atoms.

10. An epoxy curing agent of claim 9 wherein said alkylene polyamine has

only straight-chain alkylene groups.

1 1. An epoxy curing agent of claim 1 wherein said alkylene polyamine is a

polyalkylene polyamine and the ratio of primary amine equivalents of said

alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl

ether and said diglycidyl ether of an aromatic diol is essentially one.

12. An epoxy curing agent of claim 1 wherein the ratio of molar equivalents

of primary amine groups of said polyalkylene polyamine to the molar equivalents

of glycidyl groups is from about 0.85:1 to about 1.05:1.

13. An epoxy curing agent of claim 1 wherein the ratio of molar equivalents

of primary amine groups of said polyalkylene polyamine to the molar equivalents

of glycidyl groups is from about 0.90:1 to about 0.95:1.

14. An epoxy curing agent of claim 1 wherein said alkylene polyamine is a

mono-alkylene polyamine and the ratio of primary amine equivalents of said

alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl

ether and said diglycidyl ether of an aromatic diol is greater than essentially one.

15. An epoxy curing agent of claim 14 wherein said ratio is from about

1.05:1 to 2.0:1.

16. An epoxy curing agent of claim 14 wherein said ratio is from about 1.1 :1

to about 1.75:1.

17. An epoxy curing agent of claim 14 wherein said ratio is from about

1.2:1 to about 1.5:1.

18. An epoxy curing agent of claim 14 wherein said alkylene polyamine is

further comprised of a polyalkylene polyamine in a minor amount on a molar

basis of all alkylene polyamines.

19. An epoxy curing agent of claim 18 wherein the molar ratio of said mono-

alkylene polyamine to said polyalkylene polyamine is from about 6: 1 to about

2.5:1.

20. An epoxy curing agent of claim 18 wherein the molar ratio of said mono-

alkylene polyamine to said polyalkylene polyamine is from about 5:1 to about

3:1.

21. An epoxy curing agent of claim 1 wherein said ratio of epoxide

equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said

diglycidyl ether of an aromatic diol is at no time during the entire course of the

reaction less than one.

22. An epoxy curing agent of claim 1 wherein than said ratio of epoxide

equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said

reaction less the final product ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol.

23. An epoxy curing agent of claim 1 wherein said ratio of epoxide

equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said

diglycidyl ether of an aromatic .diol is maintained essentially throughout said

reaction.

24. A coating composition comprising an aqueous dispersion of an epoxy resin and an amount of the curing agent of claim 1 effective to harden said

epoxy resin, said composition being essentially free of acids.

25. A method of coating a substrate comprising contacting a surface of a

substrate with a coating composition of claim 24.

26. A method of claim 25 wherein said coating is a continuous coating and

said substrate is a rigid architectural substrate.